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VTR250 backfiring while downshifting gears.

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by fifi1980, Dec 28, 2009.

  1. Ok, I did a search for the problem I'm having and couldn't find an answer (it only happens when I shift down a gear and am engine braking.) It's not like it's only now and again, it would be every couple of minutes.....

    Is there anything I can do to fix this with my limited knowledge? Or is this a serious problem I need to have looked at right away?

    Cheers, Fi.
  2. Is the backfire midway through a downshift?
    or basically off the throttle with the clutch in and declining revs and road speed?
    Is it loud, or quiet?
    My vtr had something similar for a while, except it was a big BANG every now and then when engine braking.
    When I showed it to a mechanic he was stumped(apparently a common thing that can cause this is an exhaust leak, but this wasn't it) The only thing he could see was that the choke was on a fraction.
    He turned that off and it hasn't happened again(apart from a nice burble every now and then) According to mister mechanic man, he cant think why the choke would do it, especially as it was barely on, if it was on at all. it wasn't raising the revs, so I hadn't noticed it... maybe it was related, maybe it wasnt.
    but anyway, check yours for an exhaust leak, or the choke.
  3. I wouldnt worry bout it too much unless it suonds like your muffler is going to split, A common cause of this problem is the emission controll valve or SAS valve.
    here is some info form the Superduke forum you may find useful-----

    SAS is a system designed soley for the purpose of, I think United States, especially Californiian, emissions regs. It injects cold air into the exhaust manifold so that the any unburned fuel is combusted and therefore environmentally friendly. It also accounts for the popping/backfire phenomenon that so many SD riders like so if you eliminate the SAS then you loose this characteristic. Up to you. (Personally I find having a bike that sounds like a shotgun on every overrun up to traffic lights is not that good living in a part of London suffering from serious gun crime). Plus I find that it is a pain in the arse because I ride with such a constant sensitivity with my speed/revs/gear position that I know exactly when the "pop,bang" will occur so it distracts me from riding with my focus on what matters. Me.... I like the sound of a V twin on overrun just giving me the deep sound of Bwooooaaaaaarhhhhhhhhhh ........ fooking amazing engine braking without a pop in sight.

    It is quite likely the same for smaller 250 twin is similarly affected
  4. Sometimes it's midway, sometimes just as I shift down.......it's not really a "bang" sound, more of a loud "phut". Thanks for the advice. :)
  5. It's not a problem - it's one of the joys of motorcycle life! :grin:
  6. My VTR250 used to do it too. It's had two services in that time and no one has mentioned anything out of the ordinary. Oddly it did stop doing it though, so whether it was was fuel type or something else I have no idea but it wasn't a worry.... ****ing loved it infact ;)